1. Field of the Invention
The invention relates to a medical or dental laser instrument, especially for tooth root canal treatments.
2. Discussion of the Prior Art
A laser instrument of this type is generally known and is described for example in DE 40 38 809 C1 and in DE 42 33 744 A1.
The laser instrument according to DE 40 38 809 C1 has a second light guide at its front end that is laterally spaced from the laser instrument. Several second light guides of different cross-sectional size are associated with the laser instrument, one of which second light guides has such a small diameter that it is suitable for use in dental root canal treatment. In this known arrangement the coupling into the second light guide is effected by means of a prism that reflects the laser beams back sideways into the second light guide. An axially adjustable lens is arranged between the first light guide and the prism, the axial adjustment of the lens enabling the cross-sectional size of the laser light bundle to be matched to the respective cross-sectional size of the second light guide.
DE 42 33 744 A1 discloses a laser instrument with three light guides arranged in succession in the longitudinal direction, between each of which guides is arranged a coupling device with two lenses. In this known arrangement the middle light guide is curved. In this way it is possible to arrange the front light guide at an angle to the mid axis of the laser instrument without having to provide a deflecting device for the laser light bundle. The ends of the light guides in each case lie coaxially relative to one another in the region of the coupling devices.
The utility of a laser instrument depends among other things on the output of the laser beam bundle leaving the free end of the second light guide. In this connection an essential requirement is to guide the laser beam bundle with as little loss as possible in the light guides and to couple it to the coupling devices. In order to achieve this the numerical aperture of the light guides must not fall below a specific value. Failing this the highest possible degree of total reflection in the light guides will not be ensured as soon as the opening angle of the light cone to be transmitted exceeds the limiting angle of the light guide, which corresponds to the numerical aperture of the light guide.